refactor(hir-ty): deepen type system module

[hongjr03]

Summary

• introduce an opaque, cheaply cloned Type and a TypeSystem facade so IDE features no longer depend on Salsa query results or the internal type representation
• narrow the Salsa adapter to expression and path-resolution queries, and split inference, member operations, compatibility/packed width, and the internal type model into focused private modules
• migrate completion and extract-variable code actions to the facade, centralizing compatibility policy and removing direct arena-owner handling from callers
• move embedded tests to integration tests against the public type-system interface

Verification

• cargo test -p hir-ty
• cargo test -p ide
• cargo check --workspace
• started the vide LSP, opened a SystemVerilog document, and confirmed member completion for value. returned bar and foo